It is known by those skilled in the art that nitric oxide (NO) is a biologic mediator derived from the amino acid L-arginine. One of a family of enzymes, nitric oxide synthase (NOS), acts upon L-arginine to oxidize one of the guanidino nitrogens to NO while citrulline is formed from the remainder of the L-arginine molecule. Nitric oxide is a very short-lived free radical and is rapidly oxidized to nitrite (NO.sub.2.sup.-) and nitrate (NO.sub.3.sup.-) which is measured as the stable inactive end products of nitric oxide formation.
It is well known by those skilled in the art that multiple isoforms of the nitric oxide synthase enzyme exist and that they are generally classified into two broad categories: 1) constitutive and 2) inducible. These classes of NOS enzymes vary considerably in their size, amino acid sequence, activity and regulation. For example, cells such as neurons and vascular endothelial cells contain constitutive NOS isotypes while macrophages and vascular smooth muscle cells express an inducible NOS.
it is generally well known that small amounts of NO generated by a constitutive NOS appear to act as a messenger molecule by activating soluble guanylate cyclase and, thus, increasing intracellular guanosine, 3', 5'-cyclic monophosphate (cGMP) and the induction of biological responses that are dependent on cGMP as a secondary messenger. For example, through this mechanism, endothelial derived NO induces relaxation of vascular smooth muscle and is identified as endothelium derived relaxing factor (EDRF). Nature, Vol. 327, pp. 524-526 (1987) and Proc Natl. Acad Sci USA, Vol. 84, pp. 9265-9269 (1987). Another example includes, but is not limited by, neuronal nitric oxide which acts as a neuro transmitter by activating guanylate cyclase with important functions in the central nervous system and autonomic nervous systems. Proc Natl Acad Sci USA, Vol. 86, pp. 9030-9033 (1989) and Science, Vol. 257, p. 401 (1992).
It is generally known by those skilled in the art that the larger quantities of nitric oxide produced by the inducible nitric oxide synthase have antimicrobial and antitumor functions. J. Clin. Invest., Vol 81, pp. 1129-1136 (1989) and Science, Vol. 235, pp. 473-476 (1987), respectively. It is also known by those skilled in the art that when vascular smooth muscle cells are stimulated to express a NOS enzyme by inflammatory cytokines, the excess amounts of nitric oxides that are produced contribute to the vascular collapse seen in sepsis. FEBS Lett., Vol. 265, pp. 133-136, (1990).
Thus, it will be appreciated that nitric oxide has both normal physiologic intracellular and extracellular regulatory functions. However, excessive production of nitric oxide is detrimental. For example, stimulation of inducible nitric oxide synthesis in blood vessels by bacterial endotoxin such as for example bacterial lipopolysaccharide (LPS) and cytokines that are elevated in sepsis results in massive dilation of blood vessels and sustained hypotension commonly encountered in septic shock. Proc. Natl. Acad. Sci USA, Vol. 87, pp. 3629-32 (1990). It is known that overproduction of nitric oxide in the lungs stimulated by immune complexes directly damages the lung. J. Immunol., Vol. 148, p. 3086 (1992). Induction of nitric oxide synthase in pancreatic islets impairs insulin secretion and contributes to the onset of juvenile diabetes. J. Biol. Chem., Vol. 266, p. 21351 (1991).
It will be appreciated that there is a great need in the medical community for collective inhibition of the inducible form of NOS but not the constitutive types of NOS in humans because this would allow for a means of preventing, such as for example, the hypotensive shock seen in sepsis, without preventing the physiologic regulation of vasomotor tone or neuro transmission in the central nervous system.
We recently demonstrated that nitric oxide biosynthesis is induced in isolated human hepatocytes after stimulation with interleukin-1, tumor necrosis factor-alpha, interferon-gamma and bacterial lipopolysacharride (bacterial endotoxin). FASEB JOURNAL, Vol. 6, No. 5, page A1834 (April, 1992) and J. Exp. Med., Vol. 176, p. 261 (1992). Heretofore no human cell type was known to show increased production of nitrogen oxides when treated with cytokines. Res. Immunol., Vol. 142, p. 557 (1991). It is generally known by those skilled in the art that all attempts to induce nitric oxide synthase in human macrophages and related cells typical to those found in rodent macrophages have failed. Res. immunol., Vol. 142, p. 562, 589-90 (1991).
In spite of this background material, there remains a very real and substantial need for a cDNA clone for human tissue inducible nitric oxide synthase and a process for the molecular cloning of the same.